Field of the Invention
The present invention generally describes an improved method for laser-induced chemical vapor deposition (LCVD) of thin-film conductors on dielectric substrates.
Interconnection and/or repair of thin-film circuits is commonly required in the manufacture of integrated circuits, integrated circuit modules, and printed circuit boards. For example, open defects may occur during the manufacture of thin-film circuitry on an integrated circuit, packaging module, or printed circuit board, or an engineering change must be made. To repair these defects or make changes, it becomes necessary to interconnect separated circuit lines across an open region. This can be accomplished by depositing additional metallurgy in the form of a thin metal film deposited on the same substrate as the existing circuitry to make a change or complete the defective circuit.
LCVD of materials is a modification of conventional chemical vapor deposition (CVD), in which a focused laser is utilized as a localized heat source. An organometallic material, adsorbed or colliding at the laser heated surface is pyrolyzed to metal and liberates volatile reaction products. The actual surface temperature profile is defined by the laser power, the focal spot size, the optical and thermal properties of the substrate and of the deposited metal. The presence of metal structures on the substrate must be accounted for when using laser-driven pyrolytic techniques because they can substantially alter the surface temperature profile by thermal conduction.
Another aspect of LCVD is the metal precursor which is being used. The organometallic precursor must be volatile, easily pyrolyzed to high purity, conducting metal and decomposed at temperatures which will not damage the substrate surface. This is especially true for thermally sensitive materials such as polymers. Dimethyl gold (.beta.-diketonates) have been synthesized and successfully used to deposit high purity, conducting gold lines. The requirements for the repair of electrical opens are quite strict; the repair must be of good electrical integrity, be reliable to electrical and environmental stressing, be able to withstand subsequent chemical and physical processing and be of comparable dimensions to the existing metallurgy. LCVD gold films have been found to meet the above requirements due to the deposit's high purity, low resistivity and chemical inertness.
Laser-induced chemical deposition of gold and other metal conductors for forming and repairing thin-film conductors is described in further detail in the following publications and patents:
U.S. Pat. No. 4,880,959 to Baum et al.; "Laser chemical vapor deposition: A technique for selective area deposition" by S. D. Allen, Center for Laser Studies, University of Southern California, Jul. 17, 1981, J. Appl. Phys. 52(11), November 1981, pages 6501-6505, American Institute of Physics; "Laser chemical vapor deposition of gold" by Thomas H. Baum and Carol R. Jones, IBM Research Laboratory San Jose, Calif., Jun. 17, 1985, Appl. Phys. Lett 47(5), Sep. 1, 1985, pages 538-540, 1988 1985 American Institute of Physics; "High-resolution electron-beam induced deposition" by H. W. P. Koops, R. Weiel, D. P. Kern and T. H. Baum, IBM Thomas J. Watson Research Center, Yorktown Heights, N.Y., Oct. 20, 1987, J. Vac. Sci. Technol. B6(1). Jan./Feb. 1988, pages 477-481, 1988 American Vacuum Society; "Gold Crystal Growth by Photothermal Laser-Induced Chemical Vapor Deposition" by Toivo T. Kodas, Thomas H. Baum and Paul B. Comita, IBM Almaden Research Center, San Jose, Calif., Sep. 17, 1987, Journal of Crystal Growth 87, 1988, pages 378-382; "Kinetics of laser-induced chemical vapor deposition of gold" by T. T. Kodas, T. H. Baum and P. B. Comita, IBM Almaden Research Center, San Jose, Calif., Feb. 24, 1987, J. Appl. Phys. 62(1) Jul. 1, 1987, pages 281-286, 1987 American Institute of Physics; "Projection printing of gold micropatterns by photochemical decomposition" by Thomas H. Baum and Ernesto E. Marinero, IBM Almaden Research Center, San Jose, Calif., Sep. 9, 1986, Appl. Phys. Lett. 49(18), Nov. 3, 1986, pages 1213-1215, 1986 American Institute of Physics; and "Laser chemical vapor deposition of gold: Part II" by Thomas H. Baum, IBM Almaden Research Center, San Jose, Calif., Jun. 23, 1986, J. Vac. Sci. Technol. B4(5), Sep./Oct. 1986, pages 1187-1191, 1986 American Vacuum Society.